Downhole Cutting Tool Having A Jetted Top Bushing

ABSTRACT

A downhole cutting tool having a jetted top bushing. The cutting tool has a plurality of blades which rotate from a first, retracted position to a second, extended position. In this extended position, cutting surfaces on the blades contact the tubular wall, and rotation of the cutting tool enables cutting through the tubular. The blades are rotated by an internal piston which pushes down on portions of the blades in response to fluid flow through the tool. A plurality of fluid outlets or jets are positioned above (uphole from) the blades, whereby a portion of the fluid being pumped downhole flows out of the jets, into the annulus and onto the blades, keeping them clean and enhancing lifting of cuttings to the surface. The fluid outlet flow area may be easily changed, without disassembly of the cutting tool, by changing jets to different flow areas, or blanked off if desired.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/602,707, filed Feb. 24, 2012, for all purposes.

BACKGROUND

Various downhole tools, deployed on a drillstring, have been used to sever and/or cut windows or sections in wellbore tubulars, namely casing strings. The terms “tubulars,” “tubular strings” and “casing strings” are used in their broadest sense in this application, to include without limitation such tubulars commonly known in the industry as casing, tubing, conductors, etc.

One broad type of such tools employs a movable piston disposed in the bore within the main body of the tool. The piston is moved in a downhole direction by fluid flow through the drillstring and the bore of the tool and piston. A bore through the piston, typically having a removable jet therein, permits some fluid flow therethrough, albeit in a restricted manner, thereby pushing the piston downward and actuating a mechanism which rotates blades and cutters into position to cut the casing wall. An example of such tool is disclosed in U.S. Pat. No. 7,063,155.

One problem which can arise in connection with use of such tools is related to removal of metal cuttings (resulting from cutting and/or section milling of the casing) from the wellbore, by circulation of the drilling fluid. It can be readily understood that if not removed, such metal cuttings can form a mass sufficient to stick the cutting tool downhole. A relatively high circulating rate, combined with circular flow patterns in and around the cuttings, assists in cuttings removal.

Another issue can arise in connection with use of such tools, related to available rig pump capacity and consequent fluid (which will be called “drilling fluid” for purposes of this application) circulating rate, and available flow area through the tool, namely through the flow passage or bore of the actuating piston. It is understood that fluid flow, and resulting pressure drop, across the piston is what moves the actuating piston downward to in turn move the blades and cutters into cutting position. The actuating piston has a removable insert or jet in its bore, which enables flow area through the piston to be changed by installing jets with different hole sizes. Different flow areas may be warranted depending upon the rig's pump capacity and consequent flow rate capability. For example, a rig with low pump capacity of 1½ barrels per minute (BPM) may require a relatively small flow area through the piston, to provide sufficient pressure drop to actuate the piston. On the other hand, such small flow area restricts the total fluid flow through the tool, and consequently the fluid flow rate available to lift cuttings to the surface and clean the hole, so in settings requiring a higher flow rate and with a pump capable of delivering it, the flow rate is constrained to an unacceptably low value. While changing the piston jet to one having a larger flow area could address these situations, from a practical matter such change is difficult and time consuming to do at the well location (on the rig). This is because the tool must be disassembled to access the piston, and the tool typically comes to the rig pre-torqued and not easily disassembled on the rig. As a result, the tendency exists for the tool to be run in less than optimum hydraulic flow conditions.

SUMMARY OF THE INVENTION

The present invention comprises a downhole casing cutting and/or milling tool (referred to as a “cutting tool”) of the type having an inner operating piston with a piston bore therethrough. As is well known, the cutting tool is run downhole into a casing string (or other tubular) in a wellbore, on a drillstring. The cutting tool has one or more fluid outlets positioned above (that is, in an uphole direction from) the cutting surfaces (usually blades with attached cutters, or other types of cutting surfaces thereon). Preferably, the fluid outlets are positioned in a top sub or bushing, threadably connected to the top of the main body of the tool, which may be referred to as a “jetted top bushing.” A portion of the total drilling fluid stream (pumped down the bore of the drillstring) can flow from the bore of the drillstring into the drillstring/casing annulus, through the fluid outlets. The fluid outlets are preferably positioned and aligned so as to direct fluid in an angled-downward direction, generally toward the cutting surfaces. In the preferred embodiment, each fluid outlet comprises a threaded hole, into which various flow control inserts or jets can be installed; if desired, a “blank” can be installed, so as to completely close off the flowpath, or an insert having a desired jet diameter (essentially, a hole through which fluid will flow) can be inserted. Other embodiments may comprise inserts held in place by pins or other means known in the art. It is a simple and quick action on the jobsite to install jets, externally at the wellsite, with any desired flow area. As a result, instead of changing the size of the flow area in the inner piston to accommodate a given desired circulating rate, which as described above is a time-consuming task requiring disassembly of the cutting tool which may not be feasible on the rig, the present invention permits the size of the flow area through the jets to be changed as desired quickly and easily. The total fluid flow stream can thus be divided in an optimum manner, with a portion directed into the drillstring/casing annulus and preferably toward the cutting surfaces, and the remainder down through the bore of the tool, the piston bore, out the bottom of the tool and then back uphole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view in partial cross section, of a cutting tool embodying the present invention.

FIG. 2 is another side view of a cutting tool embodying the present invention, including the jetted top bushing.

FIG. 3 is a view showing exemplary fluid flowpaths resulting from fluid flow through the jetted top bushing.

FIG. 4 is a view of the jetted top bushing alone (separate from the remainder of the cutting tool) showing fluid flow through the jets.

FIGS. 5A and 5B are views of an alternate embodiment of the jetted top bushing.

FIG. 6 shows additional detail of a jet in position to be installed in a fluid outlet.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT(S)

With reference to the drawings, some of the presently preferred embodiments of the invention can be described.

FIG. 1 is a side view of an exemplary cutting tool embodying the principles of the present invention. The cutting tool 10 comprises a main body 20 with a lower end 22 preferably having a threaded connection 23 for connecting various tools below cutting tool 10. A longitudinal bore 21 extends through main body 20. Typically, cutting tool 10 will have both bottom (24) and top (26) bushings which are threadedly attached to main body 20. As can be seen in the drawings, especially FIG. 1, cutting tool 10 typically comprises a plurality of blades 30, each having cutting surfaces 32, typically having one or more cutters per blade, which actually contact and cut the casing or other tubular. It is understood that cutting surfaces 32 may take a number of different forms, including carbide “buttons,” carbide layers on blades 30, etc. Blades 30 are rotatably attached to main body 20 typically by pins, and are rotatable between a first position generally retracted within main body 20, and a second position as shown in FIG. 1, extending outwardly from main body 20.

Cutting tool 10 comprises a means for rotating blades from the first position to the second, outward position as shown in FIG. 1. In a presently preferred embodiment, this means for rotating comprises, generally, a piston disposed in the bore of main body 20, which is moved downward under the influence of drilling fluid being pumped downhole through the drillstring and tool, and which bears on heel portions of blades 30 and rotates them outwardly.

In more detail, piston 40 is slidably disposed in a bore in bore 21 of main body 20. Piston 40 has a bore 42 therethrough, through which fluid can be pumped. Piston 40 typically also has a removable jet 44 in bore 42, by which the flow area through the piston can be adjusted. As is well known in connection with tools of this type, fluid flow through the tool forces piston 40 in a downward position (due to the restricted flow area), the piston in turn pushes against a heel section 33 of blades 30 and rotates them outward into the position of FIG. 1.

As noted above, cutting tool 10 preferably has a jetted top bushing 26 threadably connected to its upper end. Top bushing 26 has a threaded connection 28 at its upper end, to permit attachment of the tool to a drillstring. It is understood that other embodiments of the cutting tool comprise a more unitary arrangement, with one or both of the threaded connections 23 and 28 being integral to main body 20.

As seen in the drawings, one or more, preferably a plurality, of fluid outlets 50 are arranged around the circumference of main body 20, in this example top bushing 26. Preferably, four or more fluid outlets 50 are provided and spaced equally around the circumference. Each of fluid outlets 50 is preferably adapted to engage a removable insert or jet 52, preferably by threading, pinning or other similar means well known in the art. The removable inserts or jets 52 can be “blanks,” which permit no fluid flow through the jet, or can have a hole therein forming a desired flow area therethrough. The fluid outlets 50 and jets 52 are preferably aligned generally angled downward, so that fluid flow through the fluid outlets and jets is angled downward toward cutting surfaces 32 of blades 30, as is later described. It can be readily appreciated that changing jets 52 is a relatively simple and quick task, involving no disassembly of cutting tool 10 beyond the actual changeout of the inserts, which can be done externally and without disassembly of the balance of the tool. It is therefore easy to change the resulting flow area by inserting a jet having the desired size hole for fluid flow, from no hole at all (as mentioned above, a “blank”), to one of a range of hole sizes and consequent flow area. It is understood that jets with different sizes of holes could be inserted in the fluid outlets, e.g. some of them with relatively smaller holes, some with relatively larger holes. FIG. 3 is a drawing of representative fluid flow paths (the arrowed lines) through fluid outlets 50 (and jets 52), downward toward blades 30 and surrounding area, then back uphole. The representative flow path illustrates how a circulatory path is created by fluid flow through the jets, and assists in lifting metal cuttings to the surface for removal.

FIG. 4 shows more detail of top bushing 26, fluid outlet 50 and jet 52 arrangement (separated from the rest of cutting tool 10). Fluid flow (represented by the arrowed lines) through bore 21 of top bushing 26, and out of fluid outlets 50/jets 52, is shown. Note that fluid flow from the jets is angled downward (in a downhole direction), toward the blades and cutting surfaces.

It is understood that other placements of fluid outlets 50/jets 52 is possible within the scope of the invention, all of such placements generally being at a position above (uphole from) the blades and cutting surfaces and angled so as to create a downwardly angled flow path. FIGS. 5A and 5B show one such alternative placement. In this embodiment, fluid outlets 50/jets 52 are positioned higher up (in an uphole direction) in the drillstring, above the tool joint upset in top bushing 26.

It is further understood that the invention encompasses arrangements in which fluid outlets 50 have no removable jets therein, but are simply holes drilled in top bushing 26 (or another part of cutting tool 10 uphole from blades 30). Preferably, such holes would be oriented to yield the downward flow direction desired.

As described above, the direction of fluid flow out of fluid outlets 50 and jets 52 is preferably in an angled downhole direction, toward the cutting surfaces of blades 30. However, it is understood that the invention encompasses a tool having any fluid flow direction, from generally angled downhole, to outwardly at near right angles from cutting tool 10, to angled in an uphole direction. Different of fluid outlets 50 and jets 52 could be angled in different directions (some uphole, some downhole, some at right angles), should particular applications call for such fluid flow patterns.

FIG. 6 shows additional detail of top bushing 26, fluid outlets 50, and an example of jets 52, in position to be inserted into and secured in fluid outlet 50. In the illustrated embodiment, jet 52 is threadably engaged in fluid outlet 50; as previously described, other means of attachment include pinning. etc. or any other means of removably attaching jet 52.

It can be readily understood that the placement of the jets permits quick and easy external replacement thereof, by the operator with the tool at the surface. Therefore, the flow area through the jets can be easily varied from zero (if blanked off) to any desired value, to accommodate any particular flow conditions at the wellsite.

CONCLUSION

While the preceding description contains many specificities, it is to be understood that same are presented only to describe some of the presently preferred embodiments of the invention, and not by way of limitation. Changes can be made to various aspects of the invention, without departing from the scope thereof. For example:

-   -   the size, number, and circumferential placement of the fluid         outlets and jets can be varied     -   the placement of the fluid outlets and jets along the length of         the tool can be varied     -   various combinations of jet sizes can be used     -   the jetted feature can be employed on any manner of downhole         cutting tool having a tool body which can accommodate flow         outlets and inserts     -   the jet inserts can be fixed within the fluid outlets by         threads, pins, or other means well known in the art.

Therefore, the scope of the invention is to be determined not by the illustrative examples set forth above, but by the appended claims and their legal equivalents. 

I claim:
 1. A downhole tubular cutting tool, comprising: a main body having a longitudinal bore therethrough; a plurality of blades rotatably attached to said main body and rotatable between a first position wherein said blades are substantially aligned with said main body, and a second position wherein said blades are rotated outwardly from said main body, said blades having cutting surfaces thereon; a means for rotating said blades from said first position to said second position; and a plurality of fluid outlets positioned uphole from said blades, said fluid outlets permitting fluid flow from said bore into an annulus between said cutting tool and a borehole.
 2. The cutting tool of claim 1, wherein said fluid outlets comprise removable jets disposed therein, at least one of said jets comprising a hole to yield a desired flow area therethrough, said jets being removable and replaceable from an exterior of said cutting tool.
 3. The cutting tool of claim 2, wherein fluid flow through at least one of said jets is angled downwardly toward said blades.
 4. The cutting tool of claim 2, wherein said jets are threadably engaged within said fluid outlets.
 5. The cutting tool of claim 2, wherein said jets are fixed in said fluid outlets by pins.
 6. The cutting tool of claim 1, wherein said means for rotating said blades comprises a piston slidably disposed in said bore of said main body, said piston comprising a bore therethrough, said piston moveable in a downhole direction under the influence of fluid pumped through said bore of said main body and said bore of said piston, said piston thereby bearing against a heel portion of said blades and rotating said blades to said second position.
 7. The cutting tool of claim 1, wherein said main body comprises a removable top bushing, and wherein said fluid outlets are disposed in said top bushing.
 8. The cutting tool of claim 2, wherein said main body comprises a removable top bushing, and wherein said fluid outlets are disposed in said top bushing.
 9. A downhole tubular cutting tool, comprising: a main body having a longitudinal bore therethrough; a plurality of blades rotatably attached to said main body and rotatable between a first position wherein said blades are substantially aligned with said main body, and a second position wherein said blades are rotated outwardly from said main body, said blades having cutting surfaces thereon; a piston slidably disposed in said bore of said main body, said piston comprising a bore therethrough, said piston moveable in a downhole direction under the influence of fluid pumped through said bore of said main body and said bore of said piston, said piston thereby bearing against a heel portion of said blades and rotating said blades to said second position; and a plurality of fluid outlets positioned uphole from said blades, said fluid outlets permitting fluid flow from said bore into an annulus between said cutting tool and a borehole, said fluid outlets comprising removable jets disposed therein, at least one of said jets comprising a hole to yield a desired flow area therethrough, said jets being removable and replaceable from an exterior of said cutting tool.
 10. The cutting tool of claim 9, wherein fluid flow through at least one of said jets is angled downwardly toward said blades.
 11. The cutting tool of claim 9, wherein said jets are threadably engaged within said fluid outlets.
 12. The cutting tool of claim 9, wherein said jets are fixed in said fluid outlets by pins.
 13. The cutting tool of claim 9, wherein said main body comprises a removable top bushing, and wherein said fluid outlets are disposed in said top bushing.
 14. The cutting tool of claim 13, wherein fluid flow through at least one of said jets is angled downwardly toward said blades.
 15. The cutting tool of claim 14, wherein said jets are threadably engaged within said fluid outlets.
 16. The cutting tool of claim 14, wherein said jets are fixed in said fluid outlets by pins. 